Dispersants and latexes have utility in applications such as paper coatings, colors, paints, and adhesives, as well as coatings for paper, metal, and the pharmaceutical industry. Although dispersants account for only a few percent of the total composition of paints and coating formulations, the dispersants play a critical role in the performance of such paints and coating formulations. The dispersants provide color stability and maximize pigment opacity by increasing the exposed surface area of the pigment particles, thus increasing coverage while reducing costs.
Dispersion is a complex process which involves variables including the chemistries of the solvent, resin, and pigments involved. Changes in these chemistries are associated with changes in the rheology and the resultant dispersant technology. Steric and electrostatic forces can stabilize pigment dispersions and are often accomplished with anionic and nonionic surfactants and their resulting effects on the pigment surface. These surfactants are easy to use, inexpensive, and effective at low concentrations. But, anionic surfactants are pH and salt sensitive. Adsorption of non-ionic surfactants is pH and salt insensitive, but such non-ionic surfactants need to be used in large amounts to be effective.
Other dispersant technologies use hyperdispersants which have higher molecular weights than traditional, surfactant-like dispersants. One type of such hyperdispersants are polymeric dispersants which have an anchoring group in their molecule that absorbs at the surface of the pigments and a polymeric chain that provides a steric stabilization barrier around the pigment particle. Although the polymeric dispersants absorb onto the dispersed pigments, such dispersants provide little wetting and emulsifying properties. Such dispersants are attractive is some water based-formulations because less foaming often results as compared to the surfactant-like dispersants.
Phosphate esters are often used in conjunction with dispersant technologies and are considered auxiliary dispersants since such phosphate esters are not used by themselves. The phosphate esters provide assistance with stabilization through steric interactions with the pigment particles.
Apart from the abilities of wetting and dispersing, dispersants also need to stabilize the suspended particles or the suspended particles will re-agglomerate. This stabilization is critical and difficult to accomplish, but when achieved, provides a colorant with a longer shelf life, improved color, gloss, and color compatibility.
One surfactant that exhibits these desirable dispersant properties is anionic phosphate esters which have a phosphate moiety as a head group. The anionic phosphate esters are synthesized with phosphoric acid derivatives and alcohol and have some residual phosphoric acid resulting in a pH as low as two. Anionic phosphate esters are often available in free acid form. The presence of the phosphate group in a formulation for a wetting or dispersing agent enhances the gloss and color acceptance property of a pigment in paint, reduces a viscosity increase due to aging of the paint, improves surface wetting, and provides a stable dispersion.
With the growing need for more biobased additives that can replace petroleum based products based on the desire for “greener” products, a need exists for biobased products that can be used in dispersants, coatings, and latex type products where the biobased products fulfill all the desired characteristics of the petroleum based counterparts.